1. Field of the Invention
The present invention relates to an inverter circuit device with a temperature detection circuit which can carry out overheat protection and overcurrent protection.
2. Description of the Prior Art
First, with reference to FIG. 6, operation of an inverter circuit device with a temperature detection circuit and a control circuit thereof will be briefly described.
A reference signal of a frequency according to a rotational speed setting signal is outputted from a control circuit 1 composed of a microcomputer or a DSP to a driver circuit 2. This reference signal is composed of three pulse-width modulated square waves each having a 120 degree phase difference and three square waves phase-delayed with respect to these pulse-width modulated square waves generally by 180 degrees.
The three pulse-width modulated square waves each having a 120 degree phase difference are inputted via the driver circuit 2 into control electrodes of upper arm switching elements Q1, Q2, and Q3 of an inverter circuit, and control ON/OFF of these switching elements.
In addition, pulse-width modulated square waves which are phase-delayed by 180 degrees with respect to these pulse-width modulated square waves similarly control ON/OFF of lower arm switching elements Q4, Q5, and Q6 similarly via the driver circuit 2.
Herein, diodes D1, D2, D3, D4, D5, and D6 connected to the switching elements Q1, Q2, Q3, Q4, Q5, and Q6 are free wheel diodes.
Accordingly, at output terminals of the inverter circuit which are ON/OFF-controlled by three pulse-width modulated square waves each having a 120 degree phase difference and three pulse-width modulated square waves respectively phase-delayed by 180 degrees with respect to these pulse-width modulated square waves, namely, at nodes U, V, and W between the switching elements Q1 and Q4, the switching elements Q2 and Q5, and the switching elements Q3 and Q6, a 3-phase pulse-width modulated sine voltage is obtained, and a load current which approximates a sine wave flows to a motor M.
In the aforementioned inverter circuit, when the rotational speed of the motor M is changed according to the temperature or when the temperature excessively rises, it is necessary to stop the motor M so as not to damage the inverter circuit. Therefore, a temperature detection circuit 3 is provided to detect an abnormal rise in temperature of the inverter circuit, and a detected abnormal heating signal is applied to the control signal 1 so as to stop the above-described motor M.
As a result of a change in temperature of the inverter circuit, in order to apply a temperature detection signal detected by the above-described temperature into the control signal, a dedicated terminal is required in the control circuit, therefore, the number of terminals of the control circuit increases.
In addition, in order to prevent circuit elements from being damaged when the inverter circuit temperature is overheated above a predetermined temperature, it is necessary not merely to control an electric current which flows through a switching circuit, etc., but also to stop the above-described inverter circuit from operating.
Furthermore, as shown in FIG. 7, a thermistor 3a is used to detect a temperature in the above-described temperature detection circuit 3. Priorly, an inverter circuit has been attached to a printed circuit board 4, and the above-described thermistor 3a is provided on a heat sink 5 with the inverter circuit attached. Accordingly, an accurate rise in temperature of the inverter circuit cannot be detected, and moreover, space was required.